You can perform a revert by hitting L1 or R1 along with X when you land a trick. To perform a perfect revert, you need to hit the two buttons right before you're about to land.
If you want to do a lot of these quickly, it's really easy to land a perfect revert at the very start of a level. Before you do anything else, just ollie and revert. You can keep retrying the level over and over to get 50.
Do 50 of these and the trophy will pop. After you hit your quota, you'll unlock this trophy the next time you complete a level. If you retry a level over and over again, you won't get it until you actually complete the level. (aka It won't pop immediately after the 50th.)